Stimmen - 4, Durchschnittliche Bewertung: 4.3
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Anleitung Zusammenfassung
This is done by using four connecting leads to the device and connecting the V+ and I+ leads to the anode and the V– and I– leads to the cathode as shown in Figure 1. The exact point at which the connecting leads are soldered to the device leads results in negligible temperature measurement uncertainties. In a two-wire measurement configuration, the voltage connections (point A in Figure 1) are made near or at the current source, so only two leads are actually connected to the device. Some loss in accuracy can be expected since the voltage measured at the voltmeter is the sum of the diode voltage and the voltage drop across the connecting leads. The exact temperature uncertainty will depend on the temperature range and lead resistance. For a 10-ohm lead resistance, the diode voltage will be offset by 0.1 mV, which gives a negligible temperature error at liquid helium temperature but a 50 mK error near liquid nitrogen temperature. Note the PI and CY adapter can be used only in a two-wire An excessive heat flow through the connecting leads to any temperature sensor can create a situation where the active sensing element (for the CY7/670 series this is the diode chip) is at a different temperature than the sample to which the sensor is mounted. This is then reflected as a real temperature offset between what is measured and the true sample temperature. Such temperature errors can be eliminated by proper selection and installation of the connecting leads. In order to minimize any heat flow through the leads, the leads should be of small diameter and low thermal conductivity. Phosphor-bronze or manganin wire is commonly used in sizes 32 or 36 AWG. These wires have a fairly poor thermal conductivity yet the resistivities are not so large as to create any problems in four-wire measurements. Lead wires should also be thermally anchored at several temperatures between room temperature and cryogenic temperatures to guarantee that heat is not being conducted through the leads to the sensor. A final thermal anchor at the sample itself is a good practice to assure thermal equilibrium between the sample and the temperature sensor. Note that the CU, CY, SO, and DI mounting adapters serve as their own sample thermal anchor. I the connecting leads have only a thin insulation such as vinyl acetal or other varnish type coating, a simple thermal anchor can be made by winding the wires around a copper post or other thermal mass and bonding them in place with a thin layer of CYAV varnish. There are a variety of other ways in which thermal anchors can be fabricated; a number of guidelines can be found in detail in the following references. configuration. Figure 1. Four-Wire Configuration for CY7/670 Series Sensor Installation Sensor Mounting General Comments Before installing the CY7/670 series sensor, identify which lead is the anode and which lead is the cathode by referring to the accompanying device drawings. Be sure that lead identification remains clear even after installation of the sensor, and record the serial number and location. The procedure used to solder the connecting leads is not very critical and there is very little danger in overheating the sensor. If for some reason the leads need to be cut short, they should be heat sunk with a copper clip or needle-nose pliers before soldering. Standard rosin-core electronic solder (m.p. 180C) is suitable for most applications. Applications involving the use of the SD package up to 200 °C require a higher melting point solder. A 90% Pb 10% Sn solder has been used quite successfully with a rosin flux. For all adapters except the CY, CU, and DI, the leads are gold-plated Kovar. Prolonged soldering times may cause the solder to creep up the gold- plated leads as the solder and the gold alloy. This is not detrimental to the device performance. When installing the sensor: • Make sure there are no shorts or leakage resistance between the leads or between the leads and ground. CYAV varnish or epoxy may soften varnish-type insulations so that high resistance shunts appear between wires if sufficient time for curing is not allowed. Teflon spaghetti tubing is useful for sliding over bare leads when the possibility of shorting exists. • Avoid putting stress on the device leads and allow for the contractions that occur during cooling that could fracture a solder joint or lead if installed under tension at room temperature. The CY7/670 series sensor is designed for easy removal for recalibration checks or replacement, and the following discussions for each of the adapters are geared in this direction. If semipermanent mountings are desired, the use of OBCY10 or OB-CY20 low temperature epoxy can replace the use of CYAG grease. In all cases, the mounting of the sensor should be periodically inspected to verify that good thermal contact to the mounting surface is maintained. CY7/670-SD The SD version is the basic package for the CY7/670 series sensor line, from which all other configuration...